One senator said he can’t find an “acceptable rationale” for the dismissal.

On Twitter, Sen. Jeff Flake (R-Ariz.) said he spent “several hours” trying to understand the reasoning behind the decision to fire the director less than four years into his 10-year term. Comey had been leading an FBI investigation into whether members of Trump’s campaign team had colluded with the Russian government during the presidential election.

After thinking on it, Flake said, he just couldn’t come up with an “acceptable rationale.”

I've spent the last several hours trying to find an acceptable rationale for the timing of Comey's firing. I just can't do it.

In a widely circulated memo and dismissal letter, Trump cited Comey’s handling of the investigation of Hillary Clinton’s use of a private email server as the reason for his firing but also referenced the ongoing investigation into Russia, saying: “While I greatly appreciate you informing me, on three separate occasions, that I am not under investigation, I nevertheless concur with the judgment of the Department of Justice that you are not able to effectively lead the bureau.”

Vice President Mike Pence disagreed that the timing was strange, telling reporters Wednesday morning this was the “right decision at the right time.” Pence defended Trump as a strong leader and argued “it’s time for a fresh start at the FBI.”

While many Republicansbacked the president’s decision, several GOP lawmakers also said they were troubled by the announcement. Sen. Richard Burr (R-N.C.) called Comey “a public servant of the highest order” and said his dismissal was a loss for the nation.

I am troubled by the timing and reasoning of Director Comey’s termination.

The senator said the director’s “dismissal further confuses an already difficult investigation” into Russian meddling in the presidential campaign that’s being conducted by the Senate Select Committee on Intelligence, which Burr chairs. The committee has promised to conduct an aggressive probe and said in March that the inquiry would “go wherever the intelligence leads.”

Sen. John McCain (R-Ariz.) said in a statement he was “disappointed” in the decision and noted the move only heightened the need for a “special congressional committee” to investigate.

Rep. Justin Amash (R-Mich.) said he was reviewing legislation to establish an independent commission on Russia, something leading Democrats have long sought. Amash also called the part of Trump’s dismissal letter that referenced the FBI’s investigation of his presidential rival “bizarre.”

My staff and I are reviewing legislation to establish an independent commission on Russia. The second paragraph of this letter is bizarre. https://t.co/wXeDtVIQiP

Ohio Gov. John Kasich also said he was “extremely troubled by the circumstances surrounding the dismissal.” The former Republican presidential candidate had also called for a bipartisan effort to conduct “full and fair” investigations into Russian interference. Rep. Barbara Comstock (R-Va.) reiterated that call.